Hydraulic control arrangment

ABSTRACT

A hydraulic control arrangement is disclosed for the control of a consumer, comprising at least one mechanically operated continuously adjustable distribution valve with a subsequent LUDV pressure compensator down the line. In order to lock the consumer the control arrangement is provided with a spring holding the pressure compensator piston in a closed position. Furthermore, the LS line carrying the highest load pressure of all consumers is connected to a reservoir by means of a flow regulator, wherein the pump control may also be relieved by the flow regulator in the sense of a reduction of the pumped volume. According to the invention, the LUDV pressure compensator is pressure-compensated by means of a nozzle through which a connection between the LS line and a portion of the pressure medium flow path downstream of the pump and upstream of the outlet of the pressure compensator is generated. Said nozzle is preferably integrated in the pressure compensator piston.

The invention relates to a hydraulic control arrangement for aload-independent control of a consumer according to the preamble ofclaim 1.

Mobile working implements, for instance mini excavators and compactexcavators, are increasingly equipped with hydraulic controlarrangements which distribute the volume flow of pressure medium of onesingle pump in a load-independent manner to the connected consumers. Thecontrol of these consumers is performed, for instance, via aload-pressure independent flow distribution LUDV¹ control blockincluding a plurality of valve disks each corresponding to one of theconsumers. In each valve disk a continuously adjustable distributionvalve is accommodated which is provided with a pressure-compensatingLUDV pressure compensator. The pressure medium flowing to the consumerfirst flows through a metering orifice formed by the continuouslyadjustable distribution valve and then through the pressure compensator.The control piston of this pressure compensator is loaded at its frontside with the pressure prevailing between the metering orifice and thepressure compensator. This pressure is reduced vis-à-vis the pumppressure by the largely load-pressure and pump-pressure independentpressure drop above the metering orifice. In the closing direction themaximum load pressure of all simultaneously operated hydraulic consumersis applied to the control piston of the pressure compensator. This meansthat also between the metering orifice and the pressure compensator themaximum load pressure is prevailing and that the partial amounts ofpressure medium flowing to all simultaneously operated hydraulicconsumers are reduced independently of individual load pressures of theconsumers at the same ratio when upon increase of the openingcross-sections of the metering orifice the maximum pumped amount of thecorresponding pump is reached.¹ German abbreviation (Lastdruck unabhängige Durchflussverteilung)

In the case of mini excavators and compact excavators, frequently theworking functions of boom, shovel, post and turning are operated viahydraulic pilot devices, while the functions of driving, buckling, bladeand hammer are usually operated mechanically for reasons of costs.Safety means which the driver has to activate upon leaving the driver'sseat in order to interrupt the mechanically and hydraulically operatedfunctions are legally prescribed. Interrupting the hydraulicallyoperated functions is relatively simple, because merely the supply ofthe pilot device with control oil has to be interrupted. What is moredifficult is to lock the mechanically operated functions. It is known touse mechanical positive or non-positive locks which are comparativelyexpensive to realize, however.

In U.S. Pat. No. 6,526,747 B2 a solution is disclosed in which thehydraulically and mechanically operated functions are locked by applyingthe pump pressure to the LUDV pump compensators in the closing directionand thus stopping the supply of pressure medium to the consumer. Thispump pressure acts upon operating the safety means via a distributionvalve in the load pressure line of the control block common to allconsumers, which distribution valve is operated by means of aninterrupting valve, the pressure in the control oil supply being usedfor changing over the distribution valve. Such a solution requires aconsiderable effort in terms of circuitry.

Compared to that, the object underlying the invention is to provide ahydraulic control arrangement in which the locking of the mechanicallyoperated consumers is simplified.

This object is achieved by a hydraulic control arrangement comprisingthe features of claim 1.

According to the invention, the LUDV pressure compensators correspondingto the mechanically operated distribution valves are loaded by a springacting in the closing direction. Moreover, the load pressure detectingline common to all consumers is connected to the reservoir via a flowregulator so that a small amount of control oil constantly flows offtoward the reservoir. In this load pressure line a safety valve isarranged by which the connection of the load pressure detecting line tothe flow regulator can be locked. An area upstream of the on-off valveis connected via a nozzle to a portion of the pressure medium flow pathbetween the pump and the LUDV pressure compensator.

When changing over the safety valve to a stop position the connection ofthe load pressure detecting line to the reservoir is locked and thepressure tapped off via the nozzle is effective in a rear controlchamber connected to the load pressure detecting line so that the LUDVpressure compensator is brought into its closed position. The loadpressure detecting line is connected downstream of the flow regulator toa pump control. After locking the load pressure detecting line also thecontrol pressure at the pump control drops toward the reservoir so thatthe pump can only generate the standby pressure.

The solution according to the invention excels by a very simplestructure and a good response behavior.

In two preferred embodiments of the invention the nozzle arrangedupstream of the safety valve is either integrated in the pressurecompensator, wherein the pressure applied to the inlet of the pressurecompensator is signaled to the rear control chamber by means of thisnozzle so that the pressure compensator piston is pressure-compensatedand is closed by the force of the additional spring.

In the case of the alternative solution this nozzle is provided in abranch line extending from an area upstream of the distribution valve toan area upstream of the safety valve. In this case, the pump pressureapplied upstream of the distribution valve is signaled to the rearpressure chamber.

In an embodiment of the invention the pump supplying the consumers is inthe form of a fixed displacement pump provided with a differentialpressure regulator which is controlled in response to the load pressurein the load pressure detecting line.

In an especially preferred embodiment of the invention, each of thehydraulically operated consumers is controlled by means of a pilotdevice which is provided with a separate control oil supply.

In this control oil supply an interrupting valve is provided by whichthe control oil supply of the pilot device is interrupted for lockingthe hydraulically operated consumers so that the slide valves thereofare returned to the spring-biased home position. According to theinvention, the safety valve is also actuated by the change-over of thisinterrupting valve.

Other advantageous further developments of the invention are the subjectmatter of further subclaims.

Hereinafter preferred embodiments of the invention shall be explained ingreater detail by way of schematic drawings in which:

FIG. 1 shows a circuit diagram of a control block for a mobile workingimplement including at least one mechanically controllable consumer and

FIG. 2 shows an enlarged representation of a valve disk of the controlblock from FIG. 1.

In FIG. 1 a control arrangement of a mobile working implement is shown,wherein users of the mobile working implement, for instance a mobileexcavator, are controllable via a control block 1 including valve disks2, 4. In the shown embodiment the function of a consumer, for instance ahydraulic motor 6 of a travel drive, is mechanically operated via anactuating lever and the function of a further consumer, for instance ahydraulic cylinder 8 operating the boom, is hydraulically operated.

In the shown embodiment the control block 1 is supplied with pressuremedium via a fixed displacement pump 10 the pumped flow of which iscontrolled via a differential pressure regulator 12 in response to themaximum load pressure of the operated consumers. This load pressure isguided via an LS line 14 to a control face of the differential pressureregulator 12 effective in the closing direction, while the pump pressureis applied to the control face thereof effective in the openingdirection.

Each of the valve disks 2, 4 includes a continuously adjustabledistribution valve 16 which has directional members 20, 22 and avelocity member 18. The directional members 20, 22 control the pressuremedium flow to and from the consumer and the velocity member 18determines the volume flow of the pressure medium adjustable by openinga metering orifice. Downstream of this metering orifice a LUDV pressurecompensator 24 is provided which—as described in the beginning—keeps thepressure drop above the metering orifice constant independently of theload. In the control position the individual load pressure of thecorresponding consumer is applied to each pressure compensator 24 in theopening position and in the closing position the maximum load pressuretapped off by means of the LS line 14 is applied.

In the circuit shown in FIG. 1 the distribution valve 16 of the valvedisk 2 is mechanical, for instance operated by an actuating lever,whereas the distribution valve 16 of the valve disk 4 is operated by apilot device 26 which, in principle, consists of pressure reducingvalves to the inlet of which a pressure provided by a control oil supply28 is applied and at the outlet of which a control pressure is generatedin response to the adjustment of the pilot device 26, the controlpressure being applied to control chambers 31, 33 of the distributionvalve 16 of the valve disk 4 for actuating the distribution valve 16. Inthe area between the control oil supply 28 and the pilot device 26 anelectrically operated interrupting valve 30 is provided by which thecontrol oil supply 28 can be connected to a reservoir T. In theoperating position this interrupting valve 30 is changed over so thatthe pilot device 26 is supplied with control oil.

The area downstream of the interrupting valve 30 is connected via acontrol line 32 to a control chamber of a safety valve 34 in the form ofa 2/2 port distributing valve. The safety valve 34 is biased by a springinto a switching position in which the LS line 14 is blocked. Bychanging over the interrupting valve 30 to its through-position thecontrol oil supply pressure provided by the control oil supply 28 actsin the control chamber of the safety valve 34 so that the latter isbrought into a through-position against the force of the spring.

In the area between the safety valve 34 and the differential pressureregulator 12 a flow regulator 36 is arranged by which the LS line 14 isconnected to the reservoir T. That means, in the opening position of thesafety valve 34 through the LS line a constant volume flow of controloil flows to the reservoir T whose size depends on the adjustment of theflow regulating valve 36. The pressure prevailing in the LS line 14 islimited via a pressure-limiting valve 37 arranged between the flowregulating valve 36 and the safety valve 34.

A structure of the valve disk 2 shall be explained hereinafter by way ofthe enlarged representation in FIG. 2.

Each of the afore-described valve disks 2, 4 has a pressure connection Pto which the pump pressure is applied, a reservoir connection Sconnected to the reservoir, an LS connection LS connected to the LS line14 as well as two working connections A, B connected to the consumer, inthe present case the hydraulic motor 6.

A slide valve 38 of the distribution valve 16 of the valve disk 2 isbiased into its represented home position by means of a centering springarrangement 40. The slide valve 38 is operated by an operating portion42 laterally projecting from the valve disk 2 to which an actuatinglever or the like may be hinged.

The slide valve 38 is guided in a valve bore 44 which is extended in theradial direction to a pressure chamber 46, an inlet chamber 48, twooutlet chambers 50, 52 arranged approximately symmetrically with respectto the pressure chamber 20, two working chambers 54, 56 arranged on bothsides thereof as well as to two reservoir chambers 58, 60 adjacent tothe latter.

The slide valve 16 has a central metering orifice collar 62 defining ametering orifice which forms the velocity member 18 jointly with theremaining annular land between the pressure chamber 46 and the inletchamber 48. On both sides of this metering orifice collar 62 two controlcollars 64, 66 and two reservoir collars 68, 70 of the directionalmember 20, 22 are arranged at the slide valve 38.

The pressure chamber 46 is connected to the pressure connection P andthe two reservoir chambers 58, 60 are connected to the reservoirconnection S. The inlet chamber 48 is connected to the inlet of thepressure compensator 24 via an inlet passage 72. The outlet thereof isconnected via two outlet passages 74, 76 to the outlet chamber 50, 52and the two working chambers 54, 56 are connected via working passages78, 80 to the working connection A or B, respectively.

In FIG. 2 the pressure compensator 24 is shown in its closed position.It has a pressure compensator piston 84 which is guided to be axiallymovable in a pressure compensator bore 82. The pressure compensatorpiston 84 is a step piston, the smaller piston surface being supported,in the closed position, on a shoulder 86 of the inlet passage 72. Thepressure prevailing in the outlet passages 74, 76, i.e. the loadpressure at the corresponding consumer is applied to the end face of thepressure compensator piston 84 facing said shoulder 86. The largerdiameter (see FIG. 2 above) of the pressure compensator piston 84 dipsinto a rear control chamber 88 connected to the LS connection via an LSpassage 90.

As one can especially take from the detailed representation in FIG. 2,the pressure compensator piston 84 includes an axial bore 92 opening inthe stepped-back end face, the axial bore opening in a transverse bore96 passing through the pressure compensator piston 84 in the transversedirection by means of a load detecting nozzle 94. The transverse bore isblocked in the closing and control position of the pressure compensatorpiston 84 by the circumferential walls of the pressure compensator bore86 and is not opened before the pressure compensator 24 is completelyopened. Then the control oil flows from the inlet of the pressurecompensator via the load detecting nozzle into the control chamber 88and thus into the LS line 14 so that the load pressure of the consumeris substantially applied as maximum load pressure in the LS line 14.

In the embodiment shown in FIG. 2 a further nozzle 98 via which theaxial bore 92 is constantly connected to the control chamber 88 isprovided in extension of the axial bore 92 on the other side of thetransverse bore 96.

The pressure compensator piston 84 is moreover biased via a spring 100against the shoulder 62 into its closed position in which the outercircumferential edge 102 of the stepping of the pressure compensatorpiston 84 has closed the connection between the inlet passage 72 and theoutlet passages 74, 76. The spring 100 is supported on a screw plug 104screwed into the pressure compensator bore 82.

The valve disk 4 allocated to the hydraulic function basically has thesame structure, wherein the pressure compensator piston 106 is notdesigned to have a nozzle 98, however, and thus no constant connectionis provided between the axial bore 108 and the control chamber 110.Moreover the pressure compensator piston 106 is not biased into itsclosed position by a spring.

When driving the hydraulic motor 6, the slide valve 16 is manuallyshifted by the actuating lever into an open position so that themetering orifice of the velocity member 18 is controlled to be opened.At the beginning of this control the pump pressure acting against theload pressure effective in the closing direction is applied to the inletof the pressure compensator 24. The pump pressure increases until thepressure compensator piston 84 opens the connection to the outletpassages 74, 76. Then the pressure medium can flow via the directionalmembers 20, 22 to the hydraulic motor 6 and from there back to thereservoir. If only the hydraulic motor 6 is operated, the pressurecompensator 24 is brought into the completely opened position by theload pressure prevailing at the hydraulic motor 6 so that this loadpressure is signaled to the LS line. When the boom is connected(hydraulic cylinder 8), the slide valve of the valve disk 4 iscontrolled by the pilot device 26. If the load pressure is higher at thehydraulic cylinder 8 than at the hydraulic motor 6, this higher loadpressure is signaled in the above-described manner into the controlchamber 110 of the valve disk 4 so that this higher control pressureacts upon the rear side of the pressure compensator 24 of the valve disk2. The pressure compensator piston 84 is then displaced into a controlposition in which the pressure drop above the metering orifice of thevalve disk 2 is kept constant independently of the load.

If the driver wants to leave his driver's seat, he has to operate theinterrupting valve 30 first. This is done, for example, by a switch orthe like. In this way the control oil supply of the pilot device 26 isblocked so that the distribution valve 16 of the valve disk 4 isreturned to its home position and, accordingly, the hydraulic cylinder 8is no longer driven. By changing over the interrupting valve 30 thereservoir pressure is also applied to the control line 32 so that theopen safety valve 34 is brought into its closed position. Thus, theconnection between the differential pressure regulator 12 and theindividual valve functions is interrupted. The spring chamber of thedifferential pressure regulator 12 is relieved above the flow regulator36 toward the reservoir T so that the differential pressure regulator 12only can generate the standby pressure.

Since the volume flow of control oil from the pressure compensator 24 ofthe valve disk 2 via the axial bore 82, the transverse bore 96, thenozzle 98 and via the LS line 14 is interrupted and thus no morepressure drop occurs above the pressure compensator 24 due to thiscontrol oil flow, the pressure compensator piston 84 ispressure-compensated and is returned to its closed position by the forceof the spring 100 and consequently the connection to the hydraulic motor6 is blocked.

Thus, in the afore-described embodiment also all mechanically operatedfunctions are locked by actuating the interrupting valve 30. It is alsopossible, of course, to actuate the interrupting valve 30 mechanicallyor electrically.

The dimensioning of the spring 100 and of the cross-section of thenozzle 98 is selected such that, one the one hand, a safe locking of themechanically actuated valve disks 2 is permitted but, on the other hand,the above-described LUDV function is influenced to a small extent only.

In FIG. 1 a variant of the invention is shown according to which thenozzle 98′ is not arranged in the pressure compensator piston 84 but ina branch line 112 by which the pressure medium flow path is connecteddownstream of the pump 10 and upstream of the metering orifice to aportion of the LS line 14 upstream of the safety valve 34. In the normaloperating state, i.e. when the safety valve 34 is opened, via thisnozzle 98′ a control oil volume flow continuously flows through the flowregulator 36 off to the reservoir T. When changing over the safety valve34, the pressure at the outlet of the pump acts by means of the nozzle98′ in the load detecting line 14 and thus in the control chamber 88 sothat the pressure compensator 24 is likewise returned to its closedposition.

A hydraulic control arrangement is disclosed for the control of aconsumer, comprising at least one mechanically operated continuouslyadjustable distribution valve with a subsequent LUDV pressurecompensator down the line. In order to lock the consumer the controlarrangement is provided with a spring holding the pressure compensatorpiston in a closed position. Furthermore, the LS line carrying thehighest load pressure of all consumers is connected to a reservoir bymeans of a flow regulator, wherein the pump control may also be relievedby the flow regulator in the sense of a reduction of the pumped volume.According to the invention, the LUDV pressure compensator ispressure-compensated by means of a nozzle through which a connectionbetween the LS line and a portion of the pressure medium flow pathdownstream of the pump and upstream of the outlet of the pressurecompensator is generated. Said nozzle is preferably integrated in thepressure compensator piston.

LIST OF REFERENCE NUMERALS

-   1 Control block-   2 valve disk-   4 valve disk-   6 hydraulic motor-   8 hydraulic cylinder-   10 pump-   12 differential pressure regulator-   14 LS line-   16 distribution valve-   18 velocity member-   20 directional member-   22 directional member-   24 LUDV pressure compensator-   26 pilot device-   28 control oil supply-   30 interrupting valve-   31 control chamber-   32 control passage-   33 control chamber-   34 safety valve-   36 flow control valve-   37 pressure-limiting valve-   38 slide valve-   40 centering spring arrangement-   42 operating portion-   44 valve bore-   46 pressure chamber-   48 inlet chamber-   50 outlet chamber-   52 outlet chamber-   54 working chamber-   56 working chamber-   58 reservoir chamber-   60 reservoir chamber-   62 metering orifice collar-   64 control collar-   66 control collar-   68 reservoir collar-   70 reservoir collar-   72 inlet passage-   74 outlet passage-   76 outlet passage-   78 working passage-   80 working passage-   82 pressure compensator bore-   84 pressure compensator piston-   86 shoulder-   88 rear control chamber-   90 LS passage-   92 axial bore-   94 load-detecting nozzle-   96 transverse bore-   98 nozzle-   100 spring-   102 outer circumferential edge-   104 screw plug-   106 pressure compensator piston (4)-   108 axial bore (4)-   110 control chamber (4)-   112 branch line

1. A hydraulic control arrangement for the control of a consumer,comprising at least one mechanically operated continuously adjustabledistribution valve with a subsequent pressure compensator down the lineto which the load pressure of the corresponding consumer can be appliedin the opening direction and the highest load pressure of all controlledconsumers prevailing in a rear control chamber can be applied in theclosing direction, wherein said load pressure can be carried via an LSline to a pump regulator of a pump, and comprising a safety valve uponoperation of which the pressure compensator can be brought into aclosing position for closing the connection to the consumer,characterized in that a pressure compensator piston can be held in itsclosed position by a spring, the LS line is connected to the reservoirby means of a flow control valve, the safety valve is arranged in the LSline between the flow regulator and the pressure compensator and apressure effective upon change-over of the switch valve in the controlchamber is tapped off by means of a nozzle by a pressure medium flowportion downstream of the pump and upstream of an outlet of the pressurecompensator.
 2. A control arrangement according to claim 1, wherein thenozzle is integrated in the pressure compensator piston and connects therear control chamber to the inlet of the pressure compensator.
 3. Acontrol arrangement according to claim 1, wherein the nozzle is arrangedin a branch line extending between the outlet of the pump and a portionof the LS line upstream of the safety valve.
 4. A control arrangementaccording to claim 1, wherein the pump regulator is a differentialpressure regulator and the pump is a fixed displacement pump.
 5. Acontrol arrangement according to claim 1, wherein the function of afurther consumer is hydraulically controlled by means of a pilot deviceconnected to a control oil supply which can be disconnected from thepilot device by means of an interrupting valve, wherein the safety valvecan be brought into its locked position by means of the interruptingvalve.
 6. A control arrangement according to claim 2, wherein thepressure compensator piston has an axial bore opening via a loaddetecting nozzle into a transverse bore which is controlled to be openedwhen the pressure compensator is completely opened, wherein the nozzleconnects the transverse bore to the rear control chamber.
 7. A controlarrangement according to claim 1, wherein the nozzle has a smallercross-section than a load detecting nozzle of the pressure compensatorpiston.
 8. A control arrangement according to claim 2, wherein the pumpregulator is a differential pressure regulator and the pump is a fixeddisplacement pump.
 9. A control arrangement according to claim 3,wherein the pump regulator is a differential pressure regulator and thepump is a fixed displacement pump.
 10. A control arrangement accordingto claim 2, wherein the function of a further consumer is hydraulicallycontrolled by means of a pilot device connected to a control oil supplywhich can be disconnected from the pilot device by means of aninterrupting valve, wherein the safety valve can be brought into itslocked position by means of the interrupting valve.
 11. A controlarrangement according to claim 3, wherein the function of a furtherconsumer is hydraulically controlled by means of a pilot deviceconnected to a control oil supply which can be disconnected from thepilot device by means of an interrupting valve, wherein the safety valvecan be brought into its locked position by means of the interruptingvalve.
 12. A control arrangement according to claim 4, wherein thefunction of a further consumer is hydraulically controlled by means of apilot device connected to a control oil supply which can be disconnectedfrom the pilot device by means of an interrupting valve, wherein thesafety valve can be brought into its locked position by means of theinterrupting valve.
 13. A control arrangement according to claim 2,wherein the nozzle has a smaller cross-section than a load detectingnozzle of the pressure compensator piston.
 14. A control arrangementaccording to claim 3, wherein the nozzle has a smaller cross-sectionthan a load detecting nozzle of the pressure compensator piston.
 15. Acontrol arrangement according to claim 4, wherein the nozzle has asmaller cross-section than a load detecting nozzle of the pressurecompensator piston.
 16. A control arrangement according to claim 5,wherein the nozzle has a smaller cross-section than a load detectingnozzle of the pressure compensator piston.
 17. A control arrangementaccording to claim 6, wherein the nozzle has a smaller cross-sectionthan a load detecting nozzle of the pressure compensator piston.